package com.learning.hadoop.putmerge;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.BytesWritable;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;

import java.io.IOException;

/**
 * 实现一个定制的RecordReader，这六个方法均为继承的RecordReader要求的虚函数。
 * 实现的RecordReader，为自定义的InputFormat服务
 *
 * @author Sam Sho
 */
public class WholeFileRecordReader extends RecordReader<NullWritable, BytesWritable> {

    private FileSplit fileSplit;
    private Configuration conf;
    private BytesWritable value = new BytesWritable();
    private boolean processed = false;

    @Override
    public void close() throws IOException {
        // do nothing
    }

    @Override
    public NullWritable getCurrentKey() throws IOException,
            InterruptedException {
        return NullWritable.get();
    }

    @Override
    public BytesWritable getCurrentValue() throws IOException,
            InterruptedException {
        return value;
    }

    @Override
    public float getProgress() throws IOException, InterruptedException {
        return processed ? 1.0f : 0.0f;
    }

    @Override
    public void initialize(InputSplit split, TaskAttemptContext context)
            throws IOException, InterruptedException {
        this.fileSplit = (FileSplit) split;
        this.conf = context.getConfiguration();
    }

    //process表示记录是否已经被处理过
    @Override
    public boolean nextKeyValue() throws IOException, InterruptedException {
        if (!processed) {
            byte[] contents = new byte[(int) fileSplit.getLength()];
            Path file = fileSplit.getPath();
            FileSystem fs = file.getFileSystem(conf);
            FSDataInputStream in = null;
            try {
                in = fs.open(file);
                //将file文件中 的内容放入contents数组中。使用了IOUtils实用类的readFully方法，将in流中得内容放入
                //contents字节数组中。
                IOUtils.readFully(in, contents, 0, contents.length);
                //BytesWritable是一个可用做key或value的字节序列，而ByteWritable是单个字节。
                //将value的内容设置为contents的值
                value.set(contents, 0, contents.length);
            } finally {
                IOUtils.closeStream(in);
            }
            processed = true;
            return true;
        }
        return false;
    }
}